1. Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method of transmitting a frame consisting of orthogonal frequency-division multiplexing (OFDM) symbols having various cyclic prefix (CP) lengths for each subframe in a wireless communication system.
2. Related Art
The institute of electrical and electronics engineers (IEEE) 802.16 standard provides a technique and protocol for supporting broadband wireless access. The standardization had been conducted since 1999 until the IEEE 802.16-2001 was approved in 2001. The IEEE 802.16-2001 is based on a physical layer of a single carrier (SC) called ‘WirelessMAN-SC’. The IEEE 802.16a standard was approved in 2003. In the IEEE 802.16a standard, ‘WirelessMAN-OFDM’ and ‘WirelessMAN-OFDMA’ are further added to the physical layer in addition to the ‘WirelessMAN-SC’. After completion of the IEEE 802.16a standard, the revised IEEE 802.16-2004 standard was approved in 2004. To correct bugs and errors of the IEEE 802.16-2004 standard, the IEEE 802.16-2004/Cor1 (hereinafter, IEEE 802.16e) was completed in 2005 in a format of ‘corrigendum’.
Recently, standardization on the IEEE 802.16m is in progress as a new technical standard based on the IEEE 802.16e. The IEEE 802.16m, which is a newly developed technical standard, has to be designed to support the previously designed IEEE 802.16e. That is, a technology (i.e., IEEE 802.16m) of a newly designed system has to be configured to operate by effectively incorporating a conventional technology (i.e., IEEE 802.16e). This is referred to as backward compatibility.
A base station (BS) employing a new technology performs scheduling on a radio resource with respect to a legacy user equipment (UE) or a UE employing the new technology at a bandwidth that can be supported by the BS. Scheduling of the radio resource can be performed in a logical frame consisting of a plurality of OFDM symbols in a time domain and a plurality of subchannels in a frequency domain. Therefore, there is on-going research on a frame structure in which an IEEE 802.16m system can satisfy backward compatibility with respect to an IEEE 802.16e system.
At present, as a frame structure in which the IEEE 802.16m system can satisfy backward compatibility with respect to the IEEE 802.16e system, a frame structure consisting of an OFDM symbol of which a cyclic prefix (CP) length is ⅛ times of a useful symbol time Tu is proposed. However, a frame structure consisting of an OFDM symbol having another CP length other than the ⅛ times of the useful symbol time is not clearly proposed yet.
Accordingly, when an IEEE 802.16m system supporting a frame structure consisting of an OFDM symbol having another CP length other than ⅛ Tu exists in a neighbor cell, there is a need to design the frame structure such that interference does not occur between systems in neighboring cells. In addition, there is a need to design the frame structure such that frame structures consisting of OFDM symbols having different CP lengths coexist in the same cell or subframe structures consisting of OFDM symbols having different CP lengths coexist in one frame.